The present invention relates generally to methods and apparatus for providing navigational information for visual guidance to locations of objects or points. Merely by way of example, embodiments of the present invention provide apparatus for providing guidance information using navigational graphics overlaid on a real-time video display. Such embodiments may be used, for example, in surveying, mapping, construction, or other location determination applications. The scope of embodiments of the present invention, however, is broader than this particular application and can be applied to other applications.
Traditional surveying may involve two operators working with a theodolite and range pole or a more complex optical/electronic total station. One operator generally positions the theodolite over a known point while the other operator holds the range pole at a series of known or unknown points whose locations are to be checked or measured. A prism mounted on the range pole is sighted through the theodolite and accurate angular and distance measurements to the prism are obtained at each point. The locations of the points can be determined using triangulation techniques.
An approximately analogous process takes place in modern satellite based surveying. Current techniques may involve a single operator moving about with a roving antenna/receiver or global navigation satellite system (GNSS) total station. The roving antenna may be carried on a range pole that is held by the operator. The operator stops on various points to record location information determined using signals transmitted by satellite sources. Correction data may be transmitted from a reference site through a telemetry system.
The satellite positioning system most commonly used today is the Global Positioning System (GPS), although others such as the Global Orbiting Navigation System (GLONASS) are also in use or under development. Some land based systems that use non-satellite signal sources to simulate satellite systems over a small area are also in use. GPS is based on a constellation of between 24 and 32 satellites operated by the United States Department of Defense. The satellite positions are monitored closely and act as reference points from which an antenna/receiver in the field is able to determine position information. By measuring the travel time of signals transmitted from a number of satellites, the receiver is able to determine corresponding distances from the satellites to the phase center of the antenna. The receiver is able to determine the position of the phase center of the antenna by trilateration.
Surveyors and other operators carrying out survey related work use a range of equipment and procedures. A surveyor in the field typically carries a survey control device that provides an interface to the receiver. He or she generally navigates around a site setting out or checking the layout of survey points and recording attribute information for existing features using the control device. The efficiency of surveyors and operators can be improved by simplifying the process of identifying objects or points and reducing the time required to navigate between points. Thus, there is a need for improved methods and apparatus for providing navigational information associated with locations of objects or points.